Identification of seven novel nucleotide variants in the hepatocyte nuclear factor-1alpha (TCF1) promoter region in MODY patients

Maturity onset diabetes of the young (MODY) is a heterogeneous subtype of type II diabetes mellitus. To date, five MODY genes have been identified. Mutations in the hepatocyte nuclear factor-1alpha (HNF-1alpha) gene are associated with MODY3. In the present work, we implemented the HNF-1alpha promoter region in the screening of MODY-suspect patients and identified seven variants not detected in control subjects. The family was available for the -119delG variant, and segregration between MODY and the variant is observed. Most of these variants are located in highly conserved regions and may alter HNF-1alpha expression through binding alteration of nuclear factors or other mechanisms. We demonstrate by functional studies that the transcriptional activity of the -283A>C and -218T>C variant promoters were 30% and 70% of the wild type activity, respectively. These data suggest that HNF-1alpha promoter variants could be diabetogenic mutations, and emphasize that the accurate HNF-1alpha expression is important for the maintenance of normal pancreatic beta cell function.

Genetic variation in the hepatocyte nuclear factor-3beta gene (HNF3B) does not contribute to maturity-onset diabetes of the young in French Caucasians

Mutations in genes encoding hepatocyte nuclear factor (HNF) are responsible for three of the five subtypes of maturity-onset diabetes of the young (MODY). This observation and molecular studies indicate that the HNF network is required for normal function of pancreatic beta-cells. This suggests that transcription factors involved in this complex network are candidates for genetic defects in MODY. Because the HNF-3beta gene is implicated in this network, we screened it for mutations in 21 probands of French ancestry with clinical diagnosis of MODY and early-onset type 2 diabetes. All of the five known MODY genes, HNF-4alpha, glucokinase, HNF-1alpha, HNF-1beta, and IPF1, were previously excluded as being the cause of diabetes in these families. By direct sequencing, we identified two transitions, an A-to-G at position -213 and a C-to-T at position -63 in the promoter and exon 1, respectively, of the HNF-3beta gene. A G-to-C transversion at position +32 in the intron 1 and three transitions, C-to-T at position 291, A-to-G at position 837, and G-to-A at position 1188 in the exon 3, resulting in noncoding mutations Ala97Ala, Gly279Gly, and Gln396Gln, respectively, were also identified. The allele frequencies were not significantly different between a control group and MODY probands. Familial segregation studies and linkage analysis showed that genetic variation in the HNF-3beta gene is unlikely to be the cause of early-onset type 2 diabetes in these Caucasian families.

Defective mutations in the insulin promoter factor-1 (IPF-1) gene in late-onset type 2 diabetes mellitus

Type 2 diabetes mellitus is a common disabling disease with onset in middle-aged individuals, caused by an imbalance between insulin production and action. Genetic studies point to major genetic components, but, with the exception of maturity-onset diabetes of the young (MODY), specific diabetes susceptibility genes remain to be identified. Recent studies showed that a dominant negative mutation in the insulin promoter factor-1 (IPF-1), a pancreatic beta-cell specific transcription factor, causes pancreatic agenesis and MODY. Thus, we investigated 192 French, non-MODY type 2 diabetic families for mutations in IPF-1. We identified 3 novel IPF-1 mutations, including 2 substitutions (Q59L and D76N) and an in-frame proline insertion (InsCCG243). Functional transactivation assays of these IPF-1 mutant isoforms in a beta-pancreatic tumor cell line transfected with a transcriptional reporter and IPF-1 expression plasmids demonstrate a significant inhibition of basal insulin promoter activity (stronger with the InsCCG243 mutant). We find that the InsCCG243 mutation is linked, in 2 families, to an autosomal dominant-like late-onset form of type 2 diabetes, in which insulin secretion becomes progressively impaired. The lower penetrance D76N and Q59L mutations were more prevalent and were associated with a relative risk of 12.6 for diabetes and with decreased glucose-stimulated insulin-secretion in nondiabetic subjects. We propose that IPF-1 mutations can cause MODY or apparently monogenic late-onset diabetes and that they represent a significant risk factor for type 2 diabetes in humans.

No evidence of linkage or diabetes-associated mutations in the transcription factors BETA2/NEUROD1 and PAX4 in Type II diabetes in France

AIMS/HYPOTHESIS

The identification of mutations in hepatocyte nuclear factors-1alpha, -4alpha, -1beta and insulin promoter factor-1 in maturity onset diabetes of the young (MODY) has highlighted the role that transcription factors may have in the development of diabetes. This result has focused molecular genetic studies of diabetes on other transcription factors expressed in the pancreatic beta cell. The basic helix-loop-helix transcription factor BETA2/NEUROD1 (gene symbol, NEUROD1) and the paired box homeodomain transcription factor PAX4 (PAX4) have an important role in islet and beta-cell development. We have examined the contribution of these transcription factors to the development of MODY and late-onset Type II (non-insulin-dependent) diabetes mellitus.

METHODS

Linkage studies have been done in MODY families reported to have no mutations in the five known MODY genes and in affected sibling pairs from families with late-onset Type II diabetes. Mutation screening of the coding regions of both genes was also realised by SSCP followed by sequencing in MODY patients and in probands with late-onset Type II diabetes.

RESULTS

There was no evidence of linkage with the markers for NEUROD1 and PAX4 either with MODY or late-onset Type II diabetes. Mutation screening showed single nucleotide polymorphisms, several of which resulted in amino acid substitutions: NEUROD1, Ala45Thr; PAX4, Pro321His and Pro334Ala. These amino acid sequence variants were not associated with Type II diabetes.

CONCLUSION/INTERPRETATION

Our results indicate that NEUROD1 and PAX4 are not a common cause of either MODY or late-onset Type II diabetes in the French Caucasian population.

Mutation screening in 18 Caucasian families suggest the existence of other MODY genes

Maturity-onset diabetes of the young (MODY) is a heterogeneous subtype of non-insulin-dependent diabetes mellitus characterised by early onset, autosomal dominant inheritance and a primary defect in insulin secretion. To date five MODY genes have been identified: hepatocyte nuclear factor-4 alpha (HNF-4alpha/MODY1/TCF14) on chromosome 20q, glucokinase (GCK/MODY2) on chromosome 7p, hepatocyte nuclear factor-1 alpha (HNF-1alpha/MODY3/TCF1) on chromosome 12q, insulin promoter factor-1 (IPF1/MODY4) on chromosome 13q and hepatocyte nuclear factor-1 beta (HNF-1beta/MODY5/TCF2) on chromosome 17cen-q. We have screened the HNF-4alpha, HNF-1alpha and HNF-1beta genes in members of 18 MODY kindreds who tested negative for glucokinase mutations. Five missense (G31D, R159W, A161T, R200W, R271W), one substitution at the splice donor site of intron 5 (IVS5nt + 2T-->A) and one deletion mutation (P379fsdelT) were found in the HNF-1alpha gene, but no MODY-associated mutations were found in the HNF-4alpha and HNF-1beta genes. Of 67 French MODY families that we have now studied, 42 (63%) have mutations in the glucokinase gene, 14 (21%) have mutations in the HNF-1alpha gene, and 11 (16%) have no mutations in the HNF-4alpha, IPF1 and HNF-1beta genes. Eleven families do not have mutations in the five known MODY genes suggesting that there is at least one additional locus that can cause MODY.

A missense mutation in hepatocyte nuclear factor-4 alpha, resulting in a reduced transactivation activity, in human late-onset non-insulin-dependent diabetes mellitus

Non-insulin-dependent diabetes mellitus (NIDDM) is a heterogeneous disorder characterized by hyperglycemia resulting from defects in insulin secretion and action. Recent studies have found mutations in the hepatocyte nuclear factor-4 alpha gene (HNF-4alpha) in families with maturity-onset diabetes of the young (MODY), an autosomal dominant form of diabetes characterized by early age at onset and a defect in glucose-stimulated insulin secretion. During the course of our search for susceptibility genes contributing to the more common late-onset NIDDM forms, we observed nominal evidence for linkage between NIDDM and markers in the region of the HNF-4alpha/MODY1 locus in a subset of French families with NIDDM diagnosed before 45 yr of age. Thus, we screened these families for mutations in the HNF-4alpha gene. We found a missense mutation, resulting in a valine-to-isoleucine substitution at codon 393 in a single family. This mutation cosegregated with diabetes and impaired insulin secretion, and was not present in 119 control subjects. Expression studies showed that this conservative substitution is associated with a marked reduction of transactivation activity, a result consistent with this mutation contributing to the insulin secretory defect observed in this family.